MAKING POWER COST-EFFECTIVE

By MATTHEW L. WALD, Special to the New York Times

Published: February 10, 1987

BOSTON, Feb. 9—
When utility executives boast about their accomplishments these days, they talk about the spanking new plants they did not build.

Electric utilities around the country are trying to postpone the day when new power plants are needed -by concentrating on limiting the demand for power, instead of supplying as much as they can sell.

In the process, they are employing or considering a variety of new strategies, including varying their charges by the hour, somewhat the way telephone companies do, and paying their business consumers to use less of their product.

Pioneering utilities in California and South Dakota have been successful in selling electricity at lower rates to factories, office buildings, farmers and crop processors on the condition that they be cut off at peak hours, and nationwide such practices are expected within a decade to conserve an amount of electricity equal to the output of dozens of power plants.

''When I look around at Shoreham and Midland, I thank my stars we're not in the middle of a big nuclear project,'' said J. C. Collier Jr., senior vice president of the Florida Power and Light Company, which canceled 12 reactors in the 1970's. Shoreham, on Long Island, is finished but frozen by a dispute over emergency planning, and Midland, in Michigan, was abandoned as a nuclear project but may be converted to gas. Both were also plagued by construction cost overruns. ''Me and my peer group don't care if we never build another big baseload plant.'' he said.

Reining in peak electricity use to avoid the need for new plants, or ''demand-side management,'' was the topic of a two-day conference held here last month. The meeting, organized by the Massachusetts Executive Office of Energy Resources, was attended by hundreds of utility executives, government officials and environmentalists. Adherents in New England

The idea of limiting growth in demand has gained adherents in New England as several utilities have been pushed to the edge of bankruptcy by the cost of new nuclear plants.

''No one's going to take the risk of spending $6 billion in 14 years,'' said Sharon M. Pollard, the Massachusetts Secretary of Energy Resources, referring to the cost of a new reactor.

Ms. Pollard, who said she would bet $1,000 that no one in the six-state region would break ground on a nuclear plant in this century, pointed out that no large conventional plants were under construction here either, and that very few were likely to be in the coming years.

To help in containing demand, some public utilities commissions have already instituted ''time of day'' rates in which customers pay more during specified hours.

Some companies are taking the concept a step further, however, offering contracts to commercial customers that forbid the customers to use power at peak hours or require them to cut use in such periods. Other utilities are experimenting with allowing their customers to use as much power as they like at any time of day but charging more for it at peak periods, when it costs more to produce. Aim Is to Cut Peak Use

Both strategies have the same goal: cut peak use, thereby reducing the need for new equipment and making more intense use of the equipment that is already installed.

The difficulty in shifting load away from peak hours, according to experts, is to offer incentives to users to help them recognize that the cost of electricity varies dramatically according to how much is demanded. Once a nuclear plant is built, according to Mr. Collier of Florida Power and Light, producing a kilowatt-hour of power costs only seven-tenths of a cent. But when demand exceeds the capacity of the utility's nuclear plants, the computers in its control centers turn to more expensive sources, switching them on in order of price. At the top are combustion turbines, which produce a kilowatt-hour for about 12 cents.

Under the traditional pricing system, customers are charged the same price whether it is a spring morning when heating and lighting demands are low and only the cheapest sources are generating, or a summer afternoon, when air-conditioner use forces utilities to turn on inefficient power producers. And utilities must build new plants to meet demand on the peak days, even if the equipment sits idle most of the year. 'Sending the Price Signal'

According to Paul F. Levy, chairman of the Massachusetts Department of Public Utilities, the solution is ''real time pricing,'' which he defined as ''sending the price signal that already exists in the computers of the power pool to the customers, so that hour by hour, day by day and week by week the customer knows the true value of the service being provided and can make consumption decisions based on that price.''

Some customers say they would like that option. Discussing air-conditioning, James Rogers, corporate manager for energy and environmental affairs at the Digital Equipment Corporation, said: ''We might tell our office buildings to raise the temperature one degree when it hits 12 cents a kilowatt-hour, and another degree when it hits 14 cents. That's fairly easy to do these days.''